TRANSCRIPTIONAL ACTIVATION OF THE ORIGIN OF COLIPHAGE LAMBDA-DNA REPLICATION IS REGULATED BY THE HOST DNAA INITIATOR FUNCTION

The initiator of phage lambda DNA replication, the lambda O protein, i s considered to be an analogue of the initiator of DNA replication (Dn aA) of its host, Escherichia coli. Both specifically recognize their o rigins of replication, ori lambda and oriC, respectively, and organize the assembly of specific replication complexes. However, DnaA has an additional activation function, acting on oriC-proximal DnaA-boxes, an d regulating transcription initiated at promoters in and around oriC. Here, we demonstrate that lambda plasmid replication can be synchroniz ed by a temperature shift-down that caused renaturation of the previou sly denatured DnaAts protein. Moreover, we show that elimination of th e activating DnaA function affects transcriptional activation at ori l ambda. DnaA may act by binding to DnaA-boxes, situated around the lamb da(PR) promoter; there are no such sequences in ol ia. Our results beg in to explain in molecular terms why lambda plasmid replication is Dna A-dependent [Kur et al., J. Mel. Biol. 198 (1987) 203-210] and why the initiation of phage lambda DNA replication is blocked (in E. coli dev oid of prophage Rac) after inactivation of DnaA [Wegrzyn et al., Genet ics (1995) in press].